Problem 75

075.rb

@@ -0,0 +1,47 @@
+require 'pp'
+
+lookup_triangles = {}
+m = 2
+
+while m <= 1_500_000  do
+  1.upto(m-1) do |n|
+    a = m**2 - n**2
+    b = 2*m*n
+    c = m**2 + n**2
+    perimeter = a + b + c
+    break if perimeter > 1_500_000
+    sides = [a,b,c].sort
+    sides_string = sides.join
+    lookup_triangles[sides_string] = {
+      sides: sides,
+      perimeter: perimeter
+    } if lookup_triangles[sides_string].nil?
+  end
+  m += 1
+end
+
+triangles = lookup_triangles.map{|_,v| v}.sort{|t1, t2| t1[:perimeter] <=> t2[:perimeter]}
+count = 2
+not_done = true
+while not_done
+  triangles.each_with_index do |triangle, i|
+    new_sides = [triangle[:sides][0]*count, triangle[:sides][1]*count, triangle[:sides][2]*count]
+    perimeter = new_sides.inject(&:+)
+    if i == 0 && perimeter > 1_500_000
+      not_done = false
+      break
+    elsif perimeter > 1_500_000
+      break
+    end
+    new_sides_string = new_sides.join
+    if lookup_triangles[new_sides_string].nil?
+      lookup_triangles[new_sides_string] = {
+        sides: new_sides,
+        perimeter: perimeter
+      }
+    end
+  end
+  count += 1
+end
+
+pp lookup_triangles.map{|_,v| v[:perimeter]}.group_by{|p| p}.reject{|_,v| v.count > 1}.count